Lead frame surface finishing

ABSTRACT

The present disclosure is directed to a lead frame design that includes a copper alloy base material coated with an electroplated copper layer, a precious metal, and an adhesion promotion compound. The layers compensate for scratches or surface irregularities in the base material while promoting adhesion from the lead frame to the conductive connectors, and to the encapsulant by coupling them to different layers of a multilayer coating on the lead frame. The first layer of the multilayer coating is a soft electroplated copper to smooth the surface of the base material. The second layer of the multilayer coating is a thin precious metal to facilitate a mechanical coupling between leads of the lead frame and conductive connectors. The third layer of the multilayer coating is the adhesion promotion compound for facilitating a mechanical coupling to an encapsulant around the lead frame.

BACKGROUND Technical Field

The present disclosure is directed to an improved lead frame, and inparticular, to a lead frame coating that smooths surface defects forlead frame wire bonding.

Description of the Related Art

Semiconductor packages can include a semiconductor die and a lead framethat provides an interface between external contacts through the leadframe to the semiconductor die. The semiconductor package has anencapsulant around the various elements in the semiconductor package tosecure everything into a single discrete unit. The semiconductor die istypically placed on the lead frame, and the combination is covered withencapsulant in an application chamber, with the encapsulant typicallybeing applied at high pressure or temperature, and then being allowed tocool and solidify around the package elements.

The lead frame of a semiconductor package provides a more easilyintegrated hardware interface to the semiconductor die with minimalelectrical signal degradation. In addition, the encapsulant of thesemiconductor package provides an environmental barrier to protect thesemiconductor die, as well as structural support to the leads extendingfrom the semiconductor die. Not all types of lead frames provide asufficient hardware interface to the semiconductor die with minimalelectrical signal degradation while also maintaining the environmentalprotection and structural support properties desired for thesemiconductor package. Specifically, one type of lead frame has a copperlead frame spot coated with at least 3 micrometers (μm) of silver, aswires bond weakly to bare copper. The silver lead frame coating smoothsthe surface of the lead frame to improve wire bonding to the leads ofthe lead frame with wires. However, 3 μm lead frame coatings of silversuffer from high cost and weak mechanical bonding with the encapsulant.In addition, spot coating is a time consuming process. Thus, what isneeded is a device that encourages a higher quality of electricalconnection with minimal sacrifice of environmental protection andstructural support.

BRIEF SUMMARY

The present disclosure is directed to a semiconductor package with alead frame that includes a copper alloy base material surrounded by amultilayer coating and a method of making the same. The multilayercoating includes a first coating of copper (e.g., electroplated copper),a second coating of precious metal, and a third coating of an adhesionpromotion compound. The semiconductor package is formed by attachingwires to leads of the lead frame and at least partially encapsulatingthe lead frame with an encapsulant. In some embodiments, thesemiconductor package includes a semiconductor die or chip attached tothe second coating of the lead frame.

In some embodiments, the lead frame is formed from pressing a sheet ofbase material with rollers. The rolled lead frame base material includesscratches that are smoothed by the application of the first coating. Thefirst coating provides a smooth surface onto which the second coating isapplied. To facilitate the smoothing, the lead frame base material has atypical hardness between 100-200 HV, which is greater than the hardnessof the first coating which has a typical hardness between 100-120 HV.The scratches are often less than 0.05 μm in depth. The wires are bondedto the second coating, with the third coating covering the exposed areasof the second coating. The third coating is an adhesion promoter toincrease the strength of a mechanical coupling of the encapsulant to thelead frame. In some embodiments, the third coating is formed by areaction between an exposed surface of the second coating and a reactivespecies, and the encapsulant is a resin.

In some embodiments, the first coating is copper (e.g., pure copper),the second coating is silver, and the third coating is silver oxide. Thefirst coating is greater than 0.1 μm in thickness, and in someembodiments is between 0.2 μm and 2.0 μm. The second coating is lessthan 0.1 μm in thickness, and in some embodiments is between 0.01 μm and0.3 μm. Furthermore, the wires include one of copper, gold, silver, andaluminum.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an exemplary semiconductor package.

FIG. 2A is a plan view of an exemplary lead frame reel.

FIG. 2B is a cross-sectional view of the lead frame reel.

FIGS. 3A-3D are cross-sectional views of the lead frame taken at themagnified view area BB shown in FIG. 2B, showing the various steps ofmanufacturing the lead frame.

FIG. 4 is a cross-sectional view of another embodiment of a lead frametaken at a magnified view area.

FIG. 5 is a cross-sectional view of an exemplary semiconductor package.

FIG. 6 is a flow chart of an illustrative method of the disclosure.

DETAILED DESCRIPTION

In the following description, certain specific details are set forth inorder to provide a thorough understanding of various embodiments of thedisclosure. However, one skilled in the art will understand that thedisclosure may be practiced without these specific details. In otherinstances, well-known structures associated with electronic componentsand fabrication techniques have not been described in detail to avoidunnecessarily obscuring the descriptions of the embodiments of thepresent disclosure.

Unless the context requires otherwise, throughout the specification andclaims that follow, the word “comprise” and variations thereof, such as“comprises” and “comprising,” are to be construed in an open, inclusivesense, that is, as “including, but not limited to.”

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment. Thus, the appearances of the phrases “in one embodiment” or“in an embodiment” in various places throughout this specification arenot necessarily all referring to the same embodiment. Furthermore, theparticular features, structures, or characteristics may be combined inany suitable manner in one or more embodiments.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” include plural referents unless the contentclearly dictates otherwise. It should also be noted that the term “or”is generally employed in its sense including “and/or” unless the contentclearly dictates otherwise.

As used in the specification and appended claims, the use of“correspond,” “corresponds,” and “corresponding” is intended to describea ratio of or a similarity between referenced objects. The use of“correspond” or one of its forms should not be construed to mean theexact shape or size.

Throughout the specification, the term “layer” is used in its broadestsense to include a thin film, a cap, or the like, and one layer may becomposed of multiple sub-layers.

Specific embodiments of semiconductor packages are described herein;however, the present disclosure and the reference to certain materials,dimensions, and the details and ordering of processing steps areexemplary and should not be limited to those shown.

FIG. 1 is an exemplary embodiment of the present disclosure showing across-sectional view of a package 100 comprising a lead frame 105 duringprocessing. In embodiments, the lead frame 105 includes a plurality ofleads 110 spaced from a die pad 115. A die 140 is coupled to the die pad115 of the lead frame 105. Wires 150 couple the die to the leads 110.

The die pad 115 and the leads 110 are covered by several layers, whichinclude a first coating 165 that is adjacent to the lead frame. There isa second coating 120 on the first coating 165, and a third coating 135on the second coating 120. Encapsulant (e.g., molding compound) 155 isformed around the die 140, the lead frame 105, and parts of the leads110. The encapsulant 155 may be formed to fully encapsulate the die pad155. Alternatively, the die pad and back surface of the lead frame 105may be exposed.

The die pad 115 may have a rectangular shape. However, one of skill inthe art will appreciate that the die pad 115 and the lead frame 105 canbe formed to have alternate shapes, for example a circle or a rectangle.

In some embodiments the plurality of leads 110 includes an even numberof leads 110 spaced equidistant from each other, with an identicalnumber of leads 110 on each edge of the lead frame 105. However, otherembodiments may include fewer, or more leads 110 with different spacingand arrangement in order to suit particular package requirements.

In various embodiments, the lead frame 105 is made of copper or a copperalloy, although other known metals, other conductive materials, ornonconductive materials may be used.

A first coating 165 is a conductive material and is formed on a surfaceof the lead frame 105. In embodiments, the first coating 165 is a copperor copper alloy. The first coating 165 may be formed using any suitablemethod. For example, the first coating 165 may be deposited byelectrolytic deposition, chemical-vapor deposition (CVD), sputtering,electroless plating, spray-coating, etc. In certain embodiments, thefirst coating 165 is deposited by electrolytic deposition on the surfaceof the lead frame 105. In some embodiments, the first coating 165 isselectively deposited (e.g., using a mechanical mask or some othermasking technique) so as to extend selectively only over certain areas.In embodiments, the first coating 165 has a thickness of at least about1 μm. In some embodiments, the first coating 165 has a thickness rangingfrom about 1 μm to about 2 μm.

In some embodiments, the lead frame is treated before the first coating165 is applied. Such treatments may include electrocleaning, which maybe used to remove oxides, impurities, organic materials, and the likefrom the surface of the lead frame. Other treatment steps that may beused include activation treatments. In some embodiments, activationtreatments include use of an acidic etchant solution (e.g., Descabase(Atotech Deutschland GmbH), a sulfuric acid solution, etc.). Anactivation treatment may be used to remove oxides and to activate thelead frame 105 in order to improve the adhesiveness and uniformity ofthe first coating 165. A rinsing step may be employed before thetreatment step(s), between the treatment step(s), after the treatmentstep(s) and before the first coating 165 is applied, after the firstcoating 165 is applied, or any combination thereof.

The second coating 120 is formed on at least a portion of a surface ofthe first coating 165. As shown in FIG. 1, the second coating 120 isformed on all surfaces of the lead frame 105. In various embodiments,the second coating 120 may be formed on a first surface of the leadframe 105. In some embodiments, the second coating 120 is formed on asecond surface. In other embodiments, the second coating 120 is formedon surfaces of one or more of the plurality of leads 110.

In various embodiments, the second coating 120 comprises at least onetransition metal. In some embodiments, the second coating 120 comprisesa precious metal. In further embodiments, the second coating 120comprises a group 10 or group 11 metal. In some embodiments, the secondcoating 120 comprises a group 10 metal. In other embodiments, the secondcoating 120 comprises a group 11 metal. In certain embodiments, thesecond coating 120 comprises nickel, gold, silver, or a combinationthereof. In particular embodiments, the second coating 120 comprisessilver. In embodiments, the second coating 120 has a thickness of atleast about 0.1 μm. In some embodiments, the second coating 120 has athickness ranging from about 0.1 μm to about 0.3 μm.

A die 140 is coupled to the surface of the second coating 120. Inembodiments, the die 140 may be coupled to the die pad 115 with the glueor tape 145. Then, the plurality of wires 150 are bonded between pillarsor bumps on the die 140 and contact pads on the plurality of leads 110.The coupling between the wires 150 and the die 140 may be accomplishedvia one or more electrical contacts, which may be contact pads, pillarsor solder bumps extending from the die 140 and one or more contact padsor lands on the leads 110.

A third coating 135 is formed on the second coating 120. The thirdcoating 135 is an adhesion promotion compound (e.g., a metal oxidelayer). Accordingly, embodiments of the present disclosure include adevice comprising a copper lead frame, a first coating on at least aportion of the copper lead frame, a second coating on the first coating,and a third coating on the second coating. In some embodiments, thefirst coating 165, the second coating 120 and the third coating 135 areformed at least on the leads 110 of the lead frame 105.

The third coating 135 may comprise the same metal(s) as the secondcoating 120, for example, if the third coating 135 is a metal oxidelayer. Thus, the third coating 135 may comprise at least one transitionmetal. In some embodiments, the third coating 135 comprises a preciousmetal. In some embodiments, the third coating 135 comprises a group 10or group 11 metal. In certain embodiments, the third coating 135comprises nickel oxide, gold oxide, silver oxide, or a combinationthereof. In particular embodiments, the third coating 135 comprisessilver oxide. In specific embodiments, the second coating 120 is a layerof silver and the third coating 135 is silver oxide.

In embodiments, the third coating 135 has a thickness of at least about1 nanometer (nm). In some embodiments, the third coating 135 has athickness ranging from about 1 nm to about 3 nm.

The encapsulant 155 is deposited over the plurality of wires 150, thelead frame 105, the leads 110, the die pad 115, and the third coating135 to form the package 100. In the package 100, the encapsulant 155 maycompletely surround the third coating 135. Alternatively, theencapsulant 155 may partially surround the third coating 135, as shownin FIG. 1. In some embodiments, the encapsulant 155 is formed on theplurality of wires 150, the lead frame 105, the leads 110, the die pad115, and a surface of the third coating 135.

FIG. 2A is a plan view of an exemplary lead frame reel. In themanufacturing process of a lead frame, a plurality of lead frames may beformed by taking a reel of copper alloy material and rolling the patternof the lead frames into the reel of copper alloy material.

The present disclosure is generally directed to the manufacturing oflead frames, such as the exemplary lead frames shown in FIG. 2A. A basematerial (or substrate) 100, such as copper or a copper alloy, is formedinto a lead frame reel 101. The copper alloy may be doped with anynumber of materials, and in one embodiment is doped with a material toincrease the hardness of the base material 100. Examples of some copperalloys include Cartridge Brass (Cu 70 wt. %, Zn 30 wt. %), AluminumBronze (Cu 92 wt. %, Al 8 wt. %), Beryllium Copper (Cu 98 wt. %, Be 2wt. %), Nickel Silver (Cu 78 wt. %, Ni 12 wt. %, Pb 10 wt. %),Cupronickel (Cu 70 wt. %, Ni 30 wt. %), and Gunmetal (Cu 90 wt. %, Sn 10wt. %). Other copper alloys used as the base material include unifiednumbering system C19400, C70250, and C19210. Other base materials 100may be used, such as aluminum based lead frames. The formation of thelead frame reel 101 may be by stamping, cutting, pressing, rolling,printing, or any other lead frame formation method known in the art.After formation of the lead frame reel, the base material 100 is shapedinto a plurality of lead frames 102 including lead frames 102 a, 102 b,102 c. During the manufacturing process, the lead frames 102 a, 102 b,102 c will be singulated from one another. Singulation may occur duringthe initial formation of the lead frames 102 or, as is depicted in FIG.2A, may occur at some point in time after formation of the lead frames102.

The lead frame reel 101 is copper or a copper alloy in some embodiments,which may include any number of additional elements in any quantity. Insome embodiments, additional elements are combined with copper toincrease the hardness of the lead frame reel 101 to a hardness greaterthan a hardness of pure copper. Exemplary hardness's that may beachieved include hardness's between 100 HV (Vickers Pyramid Number) to200 HV, with some embodiments including a hardness of 180 HV to 200 HV.In other embodiments, the lead frame reel 101 is formed of a differentmaterial, such as a metal, plastic, semiconductor, alloy, composite, orother material with varying levels of hardness.

Lead frames 102 a, 102 b, 102 c of the lead frames 102 are joinedtogether by reel feed guides 104. In the depicted embodiment, a firstreel feed guide 104 a is on a first side of the lead frames 102 and asecond reel feed guide 104 b is on a second side of the lead frames 102.In this configuration, the reel feed guides 104 assist the manufacturingmachinery in physically guiding the lead frames 102 along the assemblyline to receive the downstream manufacturing steps.

Each of the lead frames 102 includes a die pad (or main body) 106 and aplurality of leads 108, including a first lead 108 a and a second lead108 b. With respect to the lead frame 102 b, the die pad 106 ispositioned near a central portion of the lead frame 102 b with the leads108 radiating outward towards sides of the lead frame 102 b. Two or moreof the leads 108 may be joined together during the formation of the leadframe reel 101. Any of these leads may be electrically isolated from theother leads of the leads 108 during later steps of the manufacturingprocess. The leads 108 are formed from the same base material 100 as thedie pad 106. In other embodiments, the leads 108 are formed from adifferent material than the die pad 106. The leads 108 provide a landingfor bonding wires to couple the leads 108 to various inputs of asemiconductor die positioned on the die pad 106 of the lead frame 102 b.

FIG. 2B depicts the lead frame 102 b after an initial forming step toform the various components of the lead frame 102 b, in one embodiment.In other embodiments, FIG. 2B depicts the lead frame 102 b at anintermediate or terminal step of the manufacturing process in which thevarious components of the lead frame 102 b are formed after othermanufacturing steps. The cross-sectional view includes the first reelfeed guide 104 a, the first lead 108 a, the die pad 106, the second lead108 b, and the second reel feed guide 104 b.

FIG. 2B includes a highlighted view area BB that indicates an area formagnification from the cross-sectional view of FIG. 2B. The highlightedview area BB includes a surface of the lead frame 102 b at the secondlead 108 b. FIGS. 3A-3D depict a cross-sectional view of the highlightedview area BB shown in FIG. 2B, with each figure depicting variousmanufacturing steps of the lead frame 102 b. Although FIGS. 3A-3D depictlayers of the second lead 108 b, the same layers and base material areused for some or all of the leads 108, the die pad 106, and the reelfeed guides 104.

FIGS. 3A-3D are cross-sectional views of the lead frame 102 b taken atthe highlighted view area BB shown in FIG. 2B, showing the various stepsof manufacturing the lead frame. Specifically, FIG. 3A depicts thesecond lead 108 b of the lead frame 102 b. As discussed previously, thebase material 100 of the lead frame 102 b may be formed from any one ofmany different manufacturing methods. During formation, a surface 302 ofthe base material 100 of the lead frame 102 b may be scratched orotherwise formed with surface irregularities. For example, a rollingpress of the lead frame reel 101 may cause the surface 302 to be formedwith a plurality of surface scratches that can prevent successful wirebonding to the surface 302. In some embodiments, the surface scratchesmay be formed along a first direction of the surface 302 and not along asecond direction perpendicular to the first direction. In otherembodiments, the surface scratches or surface irregularities are in anydirection on the surface 302. Additionally, the scratches on the surface302 may be only on a first side of the lead frame 102 b, a plurality ofsides of the lead frame 102 b, or on all sides of the lead frame 102 b,including interior surfaces. The scratches or surface irregularities canbe to any depth, and in some embodiments have an average depth or a maxdepth of less than 0.05 μm.

FIG. 3B depicts the second lead 108 b coated with a first coating 304.The first coating 304 may coat only a first side of the lead frame 102b, a plurality of sides of the lead frame 102 b, or all sides of thelead frame 102 b, including interior surfaces. Fully coating all sidesof the lead frame 102 b allows for the coating application to becompleted without the use of a mask, decreasing cost, time, andcomplexity of the coating application. In some embodiments, the firstcoating 304 is a copper material. In particular embodiments, the firstcoating 304 is pure copper. In other embodiments the first coating 304is any one of the materials in the lead frame reel 101. In yet otherembodiments, the first coating 304 is any material used during themanufacturing process of the lead frame reel 101. The first coating 304may be applied to the surface 302 using any known application technique,including chemical vapor deposition (CVD), physical vapor deposition(PVD), spin coating, and in one embodiment, is applied by electroplatingthe first coating 304 to the surface 302 of the lead frame 102 b.

In some embodiments, the first coating 304 has a thickness greater thanthe depth of the scratches or surface irregularities of the surface 302.In these embodiments, the first coating 304 has an irregular first sideon the scratches or surface irregularities, and a planar second sideopposite the first side. The planar second side thus smooths the surfaceof the scratches or surface irregularities of the surface 302. In otherembodiments, the thickness of the first coating 304 is independent ofthe depth of the scratches or surface irregularities in the surface 302.In some embodiments, the first coating 304 has a thickness of at least0.1 μm, and, in some embodiments, the average or maximum thickness ofthe first coating 304 is between 0.2 μm and 2.0 μm. In otherembodiments, the average or maximum thickness of the first coating 304is greater than 2.0 μm.

The first coating 304 can have any level of hardness. In someembodiments, the first coating 304 has a hardness that is less than thehardness of the lead frame reel 101, such as a hardness of 100-120 HV. Asoft pure copper is used in one embodiment to increase the reliabilityof wire bonding to the lead frame 102 b.

FIG. 3C depicts the second lead 108 b coated with a second coating 306and a conductive connector 308 coupled to the second coating 306. Thesecond coating 306 may coat only a first side of the lead frame 102 b, aplurality of sides of the lead frame 102 b, or all sides of the leadframe 102 b, including interior surfaces. Fully coating all sides of thelead frame 102 b allows for the coating application to be completedwithout the use of a mask, decreasing cost, time, and complexity of thecoating application. In some embodiments, the second coating 306 issilver. In other embodiments the second coating 306 is any preciousmetal. In yet other embodiments, the second coating 306 is any materialused during the manufacturing process of a semiconductor package. Thesecond coating 306 may be applied to the first coating 304 using anyknown application technique, including CVD, PVD, spin coating, andelectroplating.

In some embodiments, the second coating 306 has a thickness less thanthe first coating 304. For example, the thickness of the second coating306 can be less than 0.1 μm, and, in some embodiments, the average ormaximum thickness of the second coating 306 is between 0.01 μm and 0.1μm.

FIG. 3C also includes the conductive connector 308 coupled to a portionof the second coating 306. The conductive connector 308 is any connectorused to couple the lead frame 102 b to a semiconductor die on the leadframe 102 b. In some embodiments, the conductive connector 308 is abonding wire. The conductive connector is a metal in some embodiments,such as copper, gold, silver, and aluminum. As depicted in FIG. 3C, thethin conductive connector 308 is coupled to the second coating 306 toimprove the mechanical bond strength between the conductive connector308 and the lead frame 102 b. The improved mechanical bonding can beachieved through superior chemical properties of the second coating 306as it relates to the conductive connector 308, and the softness andlevel surface of the underlying first coating 304. For example, theapplication of the second coating 306 may help prevent oxidation of thefirst coating. As oxidation of the materials used in the first coating304 (e.g., electroplated pure copper) can be detrimental to the bondingstrength of the conductive connector 308 to the lead frame 102 b, theapplication of the thin second coating 306 to prevent oxidation of thefirst coating 304 can increase the strength of the mechanical bond tothe conductive connector 308. Improved mechanical bonding can refer toan increased pull strength, an increased sheer stress resistance, orboth.

FIG. 3D depicts the second lead 108 b coated with a third coating 310.The first, second, and third coatings together comprise a multilayercoating 312 on the base material 100 of the second lead 108 b. The thirdcoating 310 may coat only a first side of the lead frame 102 b, aplurality of sides of the lead frame 102 b, or all exposed sides of thelead frame 102 b, including interior surfaces. Fully coating all sidesof the lead frame 102 b allows for the coating application to becompleted without the use of a mask, decreasing cost, time, andcomplexity of the coating application. In other embodiments, all sidesof the lead frame 102 b are coated with the third coating, includinginterior surfaces, and then a portion of the third coating is removed toallow for the conductive connector 308 to be coupled to the secondcoating 306.

The third coating 310 may be applied or fixed to the second coating 306using any known application technique, including CVD, PVD, spin coating,and electroplating. In some embodiments, the third coating 310 is formedby a reaction between the second coating 306 and a reactive species. Inparticular, in one embodiment the second coating 306 is silver and isreacted with a reactive species including oxygen using a wet process toform the third coating 310 of a silver oxide.

The third coating 310 is an adhesion promotion compound for anencapsulant. While the second coating 306 has superior bondingcharacteristics with the conductive connector 308, the second coating306 may not be optimized for mechanical bonding to an encapsulant. Incontrast, the third coating 310 provides improved adhesion to anencapsulant. For example the third coating 310 may be an oxide or ahydroxide that improves mechanical bonding with an encapsulant like amolding compound.

The improved mechanical bonding can be achieved through superiorchemical properties of the third coating 310 as it relates to anencapsulant. For example, the application of the third coating 310 mayhelp prevent sulfurization of the second coating 306. As sulfurizationof the materials used in the second coating 306 (e.g., silver) can bedetrimental to bonding strength of an encapsulant to the lead frame 102b, the application of the third coating 310 to prevent sulfurization ofthe second coating 306 can increase the strength of the mechanical bondto an encapsulant. Improved mechanical bonding can refer to an increasedpull strength, an increased sheer stress resistance, or both.

FIG. 4 depicts a main body of a substrate 100 coated with a firstcoating 305 (e.g., of a copper material). The substrate 100 is a leadframe, such as one that is copper. In particular embodiments, the firstcoating 305 is pure copper. In some embodiments, the first coating 305has a thickness greater than the depth of the scratches or surfaceirregularities of the surface 302, such as irregularity 301. As can beseen in FIG. 4, the first coating 305 has an irregular first side on thescratches or surface irregularities of the substrate 100, and anirregular second side opposite the first side. However, the irregularity(e.g., surface roughness) of the second side is less than theirregularity of the first side. In other words, the second side smoothsthe surface of the scratches or surface irregularities of the surface302. In other embodiments, the thickness of the first coating 305 isindependent of the depth of the scratches or surface irregularities inthe surface 302.

A surface irregularity of the substrate 100 is greater than a surfaceirregularity of the second layer 306, providing a smoother surface forbonding. A surface irregularity of the third layer 310 is less than thesurface irregularity of the substrate and of the second layer 306.

FIG. 5 is a cross-sectional view of an exemplary semiconductor package400 including the lead frame 102 b. The semiconductor package 400includes the lead frame 102 having the die pad 106 and the first andsecond leads 108 a, 108 b. The die pad 106 and the first and secondleads 108 a, 108 b are each coated with the multilayer coating 312.First and second conductive connectors 308 are coupled to first andsecond leads 108 a, 108 b, respectively, and to a semiconductor die 402.The semiconductor die 402 is any one of a number of integrated circuitswith input/output ports coupled to the leads 108. In addition, thesemiconductor die 402 is mechanically coupled to the die pad 106 of thelead frame 102 b by an adhesive 404. In some embodiments, the adhesive404 is directly coupled to the second coating 306. In other embodiments,the adhesive 404 is directly coupled to the die pad 106, the firstcoating 304, or the third coating 310. The semiconductor die 402 may bethermally or electrically coupled to the die pad 106 by the adhesive 404and/or other materials.

Surrounding the semiconductor die 402 is an encapsulant 406, such as amolding compound or a resin. The encapsulant 406 may provide thestructural support for the semiconductor package 400 as well asenvironmental protection. The encapsulant 406 is on or adheres to thethird coating 310 of the lead frame 102 b, in one embodiment. In otherembodiments, the encapsulant 406 is on another layer of the multilayercoating 312, or the underlying base material. The components of the leadframe 102 b may have a surface flush with a surface of the encapsulant406. In other embodiments, one or more components of the lead frame 102b protrude from a surface of the encapsulant 406. The encapsulant 406partially or completely encapsulates the semiconductor die 402.

In addition, depicted in FIG. 5 are bonding balls 408. The bonding balls408 are solder balls in one embodiment, and in other embodiments may beany conductive connector for coupling the semiconductor package 400 toexternal circuits. The bonding balls 408 are coupled to ends of theleads 108. An input or output port of the semiconductor die 402 maythereby be coupled to a circuit external to the semiconductor package400 through respective ones of the conductive connectors 308, the leads108, and the bonding balls 408, in turn.

A flow chart of an illustrative method of the disclosure is shown inFIG. 6. After an initial electrocleaning step 1000, the lead frame mayundergo an activation step 1002 followed by deposition of a firstcoating in step 1004. Then, in step 1006, the lead frame may undergo asecond activation step. A second coating is then deposited onto thesurface of the first coating in step 1008.

Next, in step 1010, an organic coating (e.g., an anti-EBO (epoxy bleedout) coating) is applied to the surface of the second coating. Such anorganic coating may reduce or eliminate epoxy bleeding out during thedie attachment. Then, in step 1012, the die is attached to the surfaceof the second coating. A third activation step 1013 is then performed,followed by forming the third coating in step 1014. One or more rinsingsteps, such as step 1016, may be employed at any suitable point in themethods disclosed.

Then, in step 1018, the encapsulant (e.g. the molding compound) isformed on the die, the wires, and the lead frame to form the package.After assembling the package, a deflashing step can be employed toremove resin flashes from the encapsulation process. Then, anelectrocleaning step, rinse step, or both may be employed.

The resulting packaging structure includes, in some embodiments, acopper first coating on a bare copper lead frame, a silver layer on thecopper first coating, and a silver oxide layer on the silver layer. Thedie is bonded via bonding wires to the silver layer, and the silveroxide layer abuts sides of the die and wires. An encapsulant surroundsat least a portion of the silver oxide layer. Thus, in some embodiments,no portion of the silver oxide layer is exposed. In other words, theencapsulant completely covers the silver oxide layer. In specificembodiments, the series of layers on the bare copper lead frame includesa copper first coating that ranges from about 1 μm to about 2 μm thick,a silver second coating that ranges from about 0.1 μm to about 0.3 μmthick, and a silver oxide third layer that ranges from about 1 nm toabout 3 nm.

In an alternative method of the disclosure, the die is attached to thesurface of the second coating after the third coating has been formed.In such methods, a portion of the third coating (e.g., corresponding tothe location at which the die is attached) is removed before attachingthe die and assembling the final package structure (e.g., wire bonding,forming the encapsulant, etc.). In embodiments where the wires are boundto the surface of the second coating, portions of the third coating areremoved that correspond to the locations at which the wires are bound.

Briefly, the alternative method optionally includes an initialelectrocleaning step and an activation step. Then, a first coating isdeposited (e.g., by electrodeposition, CVD, etc.). The lead frame maythen undergo a second activation step, and then the second coating isdeposited (e.g., by electrodeposition, CVD, etc.) onto the surface ofthe first coating. An optional third activation step may then beperformed. The third coating is then formed on the second coating (e.g.,by reacting the second coating with a reactive species, such as oxygen,by CVD, etc.). A portion of the third coating is then removed, exposingarea(s) of the second coating.

Next, an organic coating (e.g., an anti-EBO coating) is applied to theexposed surface of the second coating and the die is attached to thesurface of the second coating. After the die is attached, the finalassembly steps, including wire bonding and forming the encapsulant (e.g.the molding compound) on the die, the wires, and the lead frame, proceedto form the package. After assembling the package, a deflashing step canbe employed to remove resin flashes from the encapsulation process. Oneor more electrocleaning step, rinse step, or both, may be employed atany suitable point in the methods disclosed.

The above features describe some embodiments in which the use ofprecious metals are decreased while bonding strength of connectiveconductors to the lead frame and encapsulant to the lead frame isincreased. Other benefits will also be apparent by those of skill in theart.

The various embodiments described above can be combined to providefurther embodiments. Aspects of the embodiments can be modified, ifnecessary to employ concepts of the various patents, applications andpublications to provide yet further embodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

We claim:
 1. A device, comprising: a lead frame including: a substratehaving a main body and a plurality of leads; a first coating on the mainbody of the substrate, the first coating being copper; a second coatingon the first coating, the second coating being a precious metal; and athird coating on a first portion of the second coating, the thirdcoating being an adhesion promotion compound comprising the preciousmetal; and a resin compound on the third coating of the lead frame. 2.The device of claim 1, wherein the substrate is copper or a copperalloy, the first coating is copper, the second coating is silver, andthe third coating is silver oxide.
 3. The device of claim 1, wherein thesubstrate has a first hardness and the first coating has a secondhardness, the second hardness less than the first hardness.
 4. Thedevice of claim 3, wherein the first hardness is between 100-200 HV andthe second hardness is between 100-120 HV.
 5. The device of claim 1,wherein the first coating abuts the second coating, and the secondcoating abuts the third coating.
 6. The device of claim 1, wherein thethird coating is an oxide of the precious metal.
 7. The device of claim1, wherein a thickness of the first coating is greater than a thicknessof the second coating.
 8. The device of claim 7, wherein the thicknessof the first coating ranges from 0.2 μm to 2.0 μm and the thickness ofthe second coating ranges from 0.01 μm to 0.3 μm.
 9. The device of claim1, wherein a surface of the substrate includes surface scratches, afirst surface of the first coating being in the surface scratches and asecond surface of the first coating opposite the first surface beingplanar.
 10. The device of claim 1, further comprising a metal wirebonded directly to a second portion of the second coating.
 11. Thedevice of claim 10, wherein the metal wire includes copper, gold,silver, or aluminum.
 12. A method, comprising: forming a lead frame,including: forming a main body and a plurality of leads of a substrate;electroplating a first coating of copper or a copper alloy on the mainbody of the substrate; forming a second coating of a precious metal onthe first coating; and forming a third coating of an adhesion promotioncompound on the second coating by reacting a surface of the secondcoating with a reactive species.
 13. The method of claim 12, wherein theforming the main body and the plurality of leads includes rolling asheet of copper or a copper alloy, the rolling the sheet includingscratching a surface of the substrate.
 14. The method of claim 12,wherein the first coating is pure copper, the second coating is silverand the third coating is silver oxide.
 15. The method of claim 12,wherein the substrate has a first hardness ranging from 100 HV to 200 HVand the first coating has a second hardness ranging from 100 HV to 120HV, the second hardness being less than the first hardness.
 16. Themethod of claim 12, wherein a thickness of the first coating ranges from0.2 μm to 2.0 μm and a thickness of the second coating ranges from 0.01μm to 0.1 μm.
 17. The method of claim 12, further comprising bonding ametal wire to the second coating.
 18. A system, comprising: a lead frameincluding: a substrate having a main body; a copper coating on the mainbody of the substrate; a precious metal coating on the copper coating;and an adhesion promotion compound on a first portion of the preciousmetal coating, the adhesion promotion compound including the preciousmetal; a chip bonded to a second portion of the precious metal coatingthrough the adhesion promotion compound; a metal wire bonded to a thirdportion of the precious metal coating through the adhesion promotioncompound and bonded to the chip; and a resin compound on the lead frameand adhering directly to the adhesion promotion compound, the resincompound encapsulating the chip.
 19. The system of claim 18 wherein athickness of the copper coating is between 0.2 μm to 2.0 μm and athickness of the precious metal coating is between 0.01 μm to 0.3 μm.20. The system of claim 18 wherein the substrate has a first hardnessranging from 100 HV to 200 HV and the copper coating has a secondhardness ranging from 100 HV to 120 HV, the second hardness being lessthan the first hardness.